Visual rehabilitation with new-age rigid gas-permeable scleral contact lenses--a case series

INTRODUCTION

Primary ectatic corneal diseases usually require rigid gas-permeable (RGP) corneal contact lens wear for visual rehabilitation. As the disease progresses, it becomes increasingly difficult to fit these lenses. RGP scleral contact lenses now provide another treatment option before resorting to surgery.

CLINICAL PICTURE

Two patients with pellucid marginal degeneration and one with advanced keratoconus had failed treatment with conventional lenses.

TREATMENT

They were fitted with RGP scleral lenses.

OUTCOME

Good vision was obtained together with satisfactory fit and comfort.

CONCLUSION

RGP scleral lenses are a viable alternative to surgery in the visual rehabilitation of patients with advanced ectatic corneal disorders.

β1PIX, the PAK-interacting exchange factor, requires localization via a coiled-coil region to promote microvillus-like structures and membrane ruffles

PIX is a Rho-family guanine nucleotide exchange factor that binds PAK. We previously described two isoforms of PIX that differ in their N termini. Here, we report the identification of a new splice variant of βPIX, designated β2PIX, that is the dominant species in brain and that lacks the region of ∼120 residues with predicted coiled-coil structure at the C terminus of β1PIX. Instead, β2PIX contains a serine-rich C terminus. To determine whether these splice variants differ in their cellular function, we studied the effect of expressing these proteins in HeLa cells. We found that the coiled-coil region plays a key role in the localization of β1PIX to the cell periphery and is also responsible for PIX dimerization. Overexpression of β1, but not β2PIX, drives formation of membrane ruffles and microvillus-like structures (via activation of Rac1 and Cdc42, respectively), indicating that its function requires localized activation of these GTPases. Thus, β1PIX, like other RhoGEFs, exerts specific morphological functions that are dependent on its intracellular location and are mediated by its C-terminal dimerization domain.

Randomized clinical trial of Surodex steroid drug delivery system for cataract surgery: anterior versus posterior placement of two Surodex in the eye

OBJECTIVE

To evaluate safety and antiinflammatory efficacy of placing two Surodex (Oculex Pharmaceuticals, Inc., Sunnyvale, CA) in the eye after cataract surgery in comparison with steroid eyedrops and to compare anterior versus posterior chamber placement.

DESIGN

Randomized, masked, controlled trial.

PARTICIPANTS

One hundred four eyes of 104 Asian patients undergoing extracapsular cataract extraction with intraocular lens implantation were examined. Of these, 33 eyes of 33 patients served as control eyes (group A).

INTERVENTION

Two Surodex pellets were inserted in the anterior chamber (AC) of 35 eyes (group B), and two Surodex pellets were inserted in the ciliary sulcus of 36 eyes (group C) at the conclusion of surgery. Control eyes received neither Surodex nor a placebo implant, but were prescribed conventional 0.1% dexamethasone eyedrops four times daily for 4 weeks.

MAIN OUTCOME MEASURES

Anterior chamber flare and cells were graded clinically at the slit lamp. Anterior chamber flare was assessed objectively with the Kowa FC500 Laser Flare Meter (Kowa Co. Ltd, Tokyo, Japan). Intraocular pressure and corneal endothelial specular microscopy with morphometric cell analysis were performed for up to 1 year after surgery.

RESULTS

Lower flare meter readings occurred in both Surodex groups at all postoperative visits, as compared with the dexamethasone eyedrop group, with statistical significance at days 4 (P = 0.001), 8 (P = 0.001), and 15 (P = 0.02). No difference in flare occurred between AC and ciliary sulcus placement. Clinical slit-lamp assessment of anterior chamber flare and cells showed no difference between Surodex-treated eyes and dexamethasone-treated eyes. Nine of 33 eyes (27.3%) in group A required steroid augmentation, as opposed to 4 of 71 eyes (5.6%) in groups B and C. Inflammatory symptoms were reduced in the Surodex-treated eyes, with statistical significance for ocular discomfort (P = 0.001), photophobia (P = 0.04), and lacrimation (P = 0.01). No complications occurred with Surodex-treated eyes, and no significant difference in endothelial cell loss was noted between Surodex-treated eyes and dexamethasone-treated eyes up to 1 year after surgery.

CONCLUSIONS

Intraocular placement of two Surodex is a safe and effective treatment method to reduce intraocular inflammation after cataract surgery and clearly is superior to eyedrops in reducing inflammatory symptoms and aqueous flare as measured with the laser flare meter. No difference in efficacy between AC placement and ciliary sulcus placement of Surodex was detected in this study.

Collapsin response mediator protein switches RhoA and Rac1 morphology in N1E-115 neuroblastoma cells and is regulated by Rho kinase

The formation and directional guidance of neurites involves dynamic regulation of Rho family GTPases. Rac and Cdc42 promote neurite outgrowth, whereas Rho activation causes neurite retraction. Here we describe a role for collapsin response mediator protein (Crmp-2), a neuronal protein implicated in axonal outgrowth and a component of the semaphorin 3A pathway, in switching GTPase signaling when expressed in combination with either dominant active Rac or Rho. In neuroblastoma N1E-115 cells, co-expression of Crmp-2 with dominant active RhoA V14 induced Rac morphology, cell spreading and ruffling (and the formation of neurites). Conversely, co-expression of Crmp-2 with dominant active Rac1 V12 inhibited Rac morphology, and in cells already expressing Rac1 V12, Crmp-2 caused localized peripheral collapse, involving Rho (and Cdc42) activation. Rho kinase was a pivotal regulator of Crmp-2; Crmp-2 phosphorylation was required for Crmp-2/Rac1 V12 inhibition, but not Crmp-2/RhoA V14 induction, of Rac morphology. Thus Crmp-2, regulated by Rho kinase, promotes outgrowth and collapse in response to active Rho and Rac, respectively, reversing their usual morphological effects and providing a mechanism for dynamic modulation of growth cone guidance.

Interferon-gamma counteracts reduced endotoxin responsiveness of whole blood following trauma and cardiopulmonary bypass

Accidental as well as surgical trauma has been reported to cause reduced endotoxin responsiveness of blood in terms of cytokine production. In this study, the effect of interferon-gamma (IFN-gamma) on tumour necrosis factor-alpha (TNF-alpha)-producing capacity of whole blood after severe trauma and cardiac surgery was investigated. Blood samples of severely injured patients were collected at the first day after trauma and of cardiac surgery patients before, 4 h and 2 days after cardiopulmonary bypass (CPB). The blood samples were incubated with INF-gamma (0-100 U/ml) for 20 h and subsequently lipopolysaccharide (LPS)-induced TNF-alpha production was determined. Compared to healthy donors, LPS-induced TNF-alpha production was significantly reduced in blood cultures of trauma patients on day 1 after trauma and 4 h after CPB. Pre-incubation with IFN-gamma in vitro increased endotoxin-induced TNF-alpha production in volunteers' and all patients' blood specimens in a dose-dependent manner. IFN-gamma prompted an elevation of cytokine synthesis in CPB patients' blood which equalled that of volunteers, whereas it caused a lower rise in TNF-alpha production in blood of multiply injured patients, reaching levels of untreated donors only after incubation with 100 U/ml IFN-gamma. These experiments show that hyporesponsiveness of whole blood induced by trauma or cardiac surgery with CPB is not irreversible, but can be counteracted by the immunostimulant IFN-gamma. IFN-gamma, therefore, could be applied clinically in trauma patients or after cardiac surgery to prevent or to resolve infection complications.

Therapeutic use of Bausch & Lomb PureVision contact lenses

PURPOSE

To evaluate the Bausch & Lomb PureVision contact lens as a continuous wear contact lens for therapeutic indications in a prospective open-ended non-randomized clinical trial.

METHODS

Patients with a variety of corneal and ocular surface disease conditions presenting at the Singapore National Eye Centre who required therapeutic continuous contact lens wear were enrolled. Therapeutic indications included pain relief, corneal protection, and enhancement of corneal wound healing. Success or failure of specific treatment indications was assessed in all cases, with evaluation of lens performance and fit characteristics, and the presence of ocular complications or lens-related complications was noted.

RESULTS

There were 54 patients (54 eyes), and the mean duration of continuous contact lens wear was 1.1 months. Conditions treated included post-surgical indications (n = 36) (post-keratoplasty or ocular surface transplantation, post-LASIK or PRK surgery) bullous keratopathy (n = 7), chemical burns (n = 3), epithelial abrasions or recurrent corneal erosion syndromes (n = 3), corneal perforations (n = 3), neurotrophic ulcer (n = 1), and corneal laceration (n = 1). For the indication of corneal healing (40 eyes), improved healing was noted in 38 eyes (96%), with full healing occurring in 33 eyes (83%). For pain relief (28 eyes), 27 patients (96%) had considerable or complete pain relief, and the remaining patient reported partial pain relief. For corneal protection (21 eyes), lens wear was fully protective in all cases. The lens performance and fitting characteristics surpassed any previous therapeutic lenses used by the investigators. Complications related to contact lens wear were limited to one case of a culture-negative corneal infiltrate requiring cessation of therapeutic lens wear and one case of a loosely fit lens.

CONCLUSIONS

Our results show that the PureVision contact lens exhibits good safety and efficacy when utilized as a continuous wear therapeutic lens. With the theoretical advantage of increased oxygen transmissibility reducing the risk of hypoxia-related complications, this new lens may be one step closer to the ideal therapeutic contact lens. The PureVision contact lens is now our primary bandage lens of choice in our corneal, external disease, and refractive surgery services.

High-affinity DNA binding of HU protein from the hyperthermophile Thermotoga maritima

Prokaryotic genomes are compacted by association with small basic proteins, generating what has been termed bacterial chromatin. The ubiquitous DNA-binding protein HU serves this function. DNA-binding properties of HU from the hyperthermophilic eubacterium Thermotoga maritima are shown here to differ significantly from those characteristic of previously described HU homologs. Electrophoretic mobility shift analyses show that T. maritima HU (TmHU) binds double-stranded DNA with high affinity (K(d)=5.6(+/-0.7) nM for 37 bp DNA). Equivalent affinity is observed between 4 degrees C and 45 degrees C. TmHU has higher affinity for DNA containing a set of 4 nt loops separated by 9 bp (K(d)=1.4(+/-0.3) nM), consistent with its introduction of two DNA kinks. Using DNA probes of varying length, the optimal binding site for TmHU is estimated at 37 bp, in sharp contrast to the 9-10 bp binding site reported for other HU homologs. Alignment of >60 HU sequences demonstrates significant sequence conservation: A DNA-intercalating proline residue is almost universally conserved, and it is preceded by arginine and asparagine in most sequences, generating a highly conserved RNP motif; V substitutes for R only in HU from Thermotoga, Thermus and Deinococcus. A fivefold increase in DNA-binding affinity is observed for TmHU in which V is replaced with R (TmHU-V61R; K(d)=1.1(+/-0.2) nM), but a change in the trajectory of DNA flanking the sites of DNA intercalation is inferred from analysis of TmHU-V61R binding to DNA modified with 4 nt loops or with substitutions of 5-hydroxymethyluracil for thymine. Survival in extreme environments places unique demands on protection of genomic DNA from thermal destabilization and on access of DNA to the cellular machinery, demands that may be fulfilled by the specific DNA-binding properties of HU and by the fine structure of the bacterial chromatin.

Defects in pulmonary vasculature and perinatal lung hemorrhage in mice heterozygous null for the Forkhead Box f1 transcription factor

Decreased pulmonary expression of Forkhead Box f1 (Foxf1) transcription factor was associated with lethal alveolar hemorrhage in 55% of the Foxf1 +/- newborn mice. The severity of the pulmonary abnormalities correlates with the levels of Foxf1 mRNA. Defects in alveolarization and vasculogenesis were observed in subsets of the Foxf1 +/- mice with relatively low levels of expression from the normal Foxf1 allele. Lung hemorrhage was coincident with disruption of the mesenchymal-epithelial cell interfaces in the alveolar and bronchiolar regions of the lung parenchyma and was associated with increased apoptosis and reduced surfactant protein B (SP-B) expression. Finally, the lung defect associated with the Foxf1 +/- mutation was accompanied by reduced expression of vascular endothelial growth factor (VEGF), the VEGF receptor 2 (Flk-1), bone morphogenetic protein 4 (Bmp-4), and the transcription factors of the Brachyury T-Box family (Tbx2-Tbx5) and Lung Kruppel-like Factor. Reduction in the level of Foxf1 caused neonatal pulmonary hemorrhage and abnormalities in alveologenesis, implicating this transcription factor in the regulation of mesenchyme-epithelial interaction critical for lung morphogenesis.

alpha2-chimaerin, a Cdc42/Rac1 regulator, is selectively expressed in the rat embryonic nervous system and is involved in neuritogenesis in N1E-115 neuroblastoma cells

Neuronal differentiation involves Rac and Cdc42 GTPases. alpha-Chimaerin, a Rac/Cdc42 regulator, occurs as alpha1- and alternatively spliced Src homology 2 (SH2) domain-containing alpha2-isoforms. alpha2-chimaerin mRNA was highly expressed in the rat embryonic nervous system, especially in early postmitotic neurons. alpha1-chimaerin mRNA was undetectable before embryonic day 16.5. Adult alpha2-chimaerin mRNA was restricted to neurons within specific brain regions, with highest expression in the entorhinal cortex. alpha2-chimaerin protein localized to neuronal perikarya, dendrites, and axons. The overall pattern of alpha2-chimaerin mRNA expression resembles that of cyclin-dependent kinase regulator p35 (CDK5/p35) which participates in neuronal differentiation and with which chimaerin interacts. To determine whether alpha2-chimaerin may have a role in neuronal differentiation and the relevance of the SH2 domain, the morphological effects of both chimaerin isoforms were investigated in N1E-115 neuroblastoma cells. When plated on poly-lysine, transient alpha2-chimaerin but not alpha1-chimaerin transfectants formed neurites. Permanent alpha2-chimaerin transfectants generated neurites whether or not they were stimulated by serum starvation, and many cells were enlarged. Permanent alpha1-chimaerin transfectants displayed numerous microspikes and contained F-actin clusters, a Cdc42-phenotype, but generated few neurites. In neuroblastoma cells, alpha2-chimaerin was predominantly soluble with some being membrane-associated, whereas alpha1-chimaerin was absent from the cytosol, being membrane- and cytoskeleton-associated, paralleling their subcellular distribution in brain. Transient transfection with alpha2-chimaerin mutated in the SH2 domain (N94H) generated an alpha1-chimaerin-like phenotype, protein partitioned in the particulate fraction, and in NGF-stimulated pheochromocytoma cell line 12 (PC12) cells, neurite formation was inhibited. These results indicate a role for alpha2-chimaerin in morphological differentiation for which its SH2 domain is vital.

Blot overlays with 32P-labeled fusion proteins

Proteins labeled with 32P can be used as sensitive "prime" in blot overlays to detect binding proteins or domains. Small G-protein Ras can bind GTP with extremely high affinity (Kd approximately 10(-11)-10(-12) M) in the presence of Mg2+. We have taken advantage of this property of Ras to develop a vector that expresses proteins of interest such as glutathione S-transferase (GST)/Ras fusion proteins for noncovalent labeling with [gamma-32P]GTP. The labeling efficiency of this method is >60% and involves a single short incubation step. We have previously identified several binding proteins for the second SH3 domain of the adaptor Nck using this method. Here we illustrate the overlay method using the GST/Ras system and compare results with the SH3 domain labeled by phosphorylation with [gamma-32P]ATP. Both methods are similarly specific and sensitive; however, we show that signals are dependent primarily on GST-mediated probe dimerization. These dimeric probes allow a more stable probe-target complex similar to immunoglobulin interactions, thus significantly improving the sensitivity of the technique.

Phosphorylation of a novel myosin binding subunit of protein phosphatase 1 reveals a conserved mechanism in the regulation of actin cytoskeleton

The myotonic dystrophy kinase-related kinases RhoA binding kinase and myotonic dystrophy kinase-related Cdc42 binding kinase (MRCK) are effectors of RhoA and Cdc42, respectively, for actin reorganization. Using substrate screening in various tissues, we uncovered two major substrates, p130 and p85, for MRCKalpha-kinase. p130 is identified as myosin binding subunit p130, whereas p85 is a novel related protein. p85 contains N-terminal ankyrin repeats, an alpha-helical C terminus with leucine repeats, and a centrally located conserved motif with the MRCKalpha-kinase phosphorylation site. Like MBS130, p85 is specifically associated with protein phosphatase 1delta (PP1delta), and this requires the N terminus, including the ankyrin repeats. This association is required for the regulation of both the catalytic activities and the assembly of actin cytoskeleton. The N terminus, in association with PP1delta, is essential for actin depolymerization, whereas the C terminus antagonizes this action. The C-terminal effects consist of two independent events that involved both the conserved phosphorylation inhibitory motif and the alpha-helical leucine repeats. The former was able to interact with PP1delta only in the phosphorylated state and result in inactivation of PP1delta activity. This provides further evidence that phosphorylation of a myosin binding subunit protein by specific kinases confers conformational changes in a highly conserved region that plays an essential role in the regulation of its catalytic subunit activities.

The tyrosine kinase ACK1 associates with clathrin-coated vesicles through a binding motif shared by arrestin and other adaptors

One target for the small GTPase Cdc42 is the nonreceptor tyrosine kinase activated Cdc42-associated kinase (ACK), which binds selectively to Cdc42.GTP. We report that ACK1 can associate directly with the heavy chain of clathrin. A central region in ACK1 containing a conserved motif behaves as a clathrin adaptor and competes with beta-arrestin for a common binding site on the clathrin N-terminal head domain. Overexpressed ACK1 perturbs clathrin distribution, an activity dependent on the presence of C-terminal "adaptor" sequences that are also present in the related nonkinase gene 33. ACK1 interacts with the adaptor Nck via SH3 interactions but does not form a trimeric complex with p21-activated serine/threonine kinase, which also binds Nck. Stable low level expression of green fluorescent protein-ACK1 in NIH 3T3 cells has been used to localize ACK1 to clathrin-containing vesicles. The co-localization of ACK1 in vivo with clathrin and AP-2 indicates that it participates in trafficking, underlying an ability to increase receptor-mediated transferrin uptake.

Protein kinases required for segregation of vimentin filaments in mitotic process

Vimentin, one of type III intermediate filament (IF) proteins, is expressed not only in mesenchymal cells but also in most types of tumor cells. In the present study, we introduced several types of vimentin mutated at putative phosphorylation sites in its amino-terminal head domain into type III IF-negative T24 cells. Site-specific mutation induced the formation of an unusually long bridge-like IF structure between the unseparated daughter cells, although these mutants formed the filament network similar to wild type in interphase cells. Together with sites phosphorylated by Rho-kinase and protein kinase C (PKC), vimentin-Ser72, which can not be phosphorylated by any known vimentin kinase, was one of the mutation sites essential for this phenotype. We further demonstrated that vimentin-Ser72 was phosphorylated specifically at the cleavage furrow during cytokinesis. These observations suggest the existence of a novel protein kinase responsible for vimentin filament separation through the cleavage furrow-specific vimentin phosphorylation. We propose that Rho-kinase, PKC, and an unidentified vimentin-Ser72 kinase may play important roles in vimentin filament separation during cytokinesis.

The mechanism of PAK activation. Autophosphorylation events in both regulatory and kinase domains control activity

The p21-activated kinases (PAKs), in common with many kinases, undergo multiple autophosphorylation events upon interaction with appropriate activators. The Cdc42-induced phosphorylation of PAK serves in part to dissociate the kinase from its partners PIX and Nck. Here we investigate in detail how autophosphorylation events affect the catalytic activity of PAK by altering the autophosphorylation sites in both alpha- and betaPAK. Both in vivo and in vitro analyses demonstrate that, although most phosphorylation events in the PAK N-terminal regulatory domain play no direct role in activation, a phosphorylation of alphaPAK serine 144 or betaPAK serine 139, which lie in the kinase inhibitory domain, significantly contribute to activation. By contrast, sphingosine-mediated activation is independent of this residue, indicating a different mode of activation. Thus two autophosphorylation sites direct activation while three others control association with focal complexes via PIX and Nck.

Transcription factors in mouse lung development and function

Development of the mouse lung initiates on day 9.5 postcoitum from the laryngotracheal groove and involves mesenchymal-epithelial interactions, in particular, those between the splanchnic mesoderm and epithelial cells (derived from foregut endoderm) that induce cellular proliferation, migration, and differentiation, resulting in branching morphogenesis. This developmental process mediates formation of the pulmonary bronchiole tree and integrates a terminal alveolar region with an extensive endothelial capillary bed, which facilitates efficient gas exchange with the circulatory system. The major function of the mesenchymal-epithelial signaling is to potentiate the activity or expression of cell type-specific transcription factors in the developing lung, which, in turn, cooperatively bind to distinct promoter regions and activate target gene expression. In this review, we focus on the role of transcription factors in lung morphogenesis and the maintenance of differentiated gene expression. These lung transcription factors include forkhead box A2 [also known as hepatocyte nuclear factor (HNF)-3beta], HNF-3/forkhead homolog (HFH)-8 [also known as FoxF1 or forkhead-related activator-1], HNF-3/forkhead homolog-4 (also known as FoxJ1), thyroid transcription factor-1 (Nkx2.1), and homeodomain box A5 transcription factors, the zinc finger Gli (mouse homologs of the Drosophila cubitus interruptus) and GATA transcription factors, and the basic helix-loop-helix Pod1 transcription factor. We summarize the phenotypes of transgenic and knockout mouse models, which define important functions of these transcription factors in cellular differentiation and lung branching morphogenesis.

Signal therapy for RAS-induced cancers in combination of AG 879 and PP1, specific inhibitors for ErbB2 and Src family kinases, that block PAK activation

BACKGROUND

Both EGF family ligands and ErbB family receptor kinases act upstream of RAS to induce mitogenesis of normal cells, such as NIH 3T3 fibroblasts. However, oncogenically mutated RAS, such as v-Ha-RAS is constitutively activated and therefore no longer requires these ligands or receptors for its activation. Nevertheless, it up-regulates the expression of these EGF family ligands. To understand the biologic significance of RAS-induced up-regulation of these ligands in both RAS-induced PAK activation and malignant transformation, we have conducted the following studies, based on the previous observations that (1) the N-terminal SH3 domain of PIX selectively binds a Pro-rich domain of 18 amino acids of PAKs, CDC42/Rac-dependent Ser/Thr kinase family, and (2) this specific interaction is essential for both PAK activation and membrane ruffling

RESULTS

Using four distinct, cell-permeable, and highly specific inhibitors, namely WR-PAK18, which blocks the PAK-PIX interaction; AG 1478, which inhibits ErbB1 kinase activity; and AG 825 or AG 879, which inhibits ErbB2 kinase activity, we demonstrate that (1) the PAK-PIX interaction is essential for v-Ha-RAS-induced malignant transformation; (2) v-Ha-RAS requires not only ErbB1 but also ErbB2, which are activated through two independent autocrine pathways to induce both the PIX/Rac/CDC42-dependent PAK activation and malignant transformation in vitro; and (3) a combination of AG 879 and the Src family kinase-specific inhibitor PP1 suppresses almost completely the growth of RAS-induced sarcomas in nude mice.

CONCLUSION

These findings not only change our conventional view on the role of these RAS-inducible ligands and ErbB family receptors (serving as RAS activators) but also suggest a new avenue for the treatment of RAS-associated cancers by a combination of inhibitors specific for ERbB, Src, or PAK family kinases.

Optimized analytical method for cyclosporin A by high-performance liquid chromatography-electrospray ionization mass spectrometry

The Micromass Platform LCZ mass detector parameters were optimized for simultaneous recording of the protonated (CsA-H+), sodium adduct (CsA-Na+) and potassium adduct (CsA-K+) of cyclosporin A eluted from a Symmetry Shield RP8 column. The optimized procedure allows a precise analysis of CsA in whole blood or serum without removal of salts prior to analysis. The ratio of the three forms of CsA varied depending on the assay condition and the types of specimens being analyzed. The summation of three ionic forms of CsA detected by LC-ESI-MS is a reliable and simple method to assess CsA concentration in the blood.

Differential expression of forkhead box transcription factors following butylated hydroxytoluene lung injury

The forkhead box (Fox) proteins are a growing family of transcription factors that have important roles in cellular proliferation and differentiation and in organ morphogenesis. The Fox family members hepatocyte nuclear factor (HNF)-3beta (Foxa2) and HNF-3/forkhead homolog (HFH)-8 (FREAC-1, Foxf1) are expressed in adult pulmonary epithelial and mesenchymal cells, respectively, but these cells display only low expression levels of the proliferation-specific HFH-11B gene (Trident, Foxm1b). The regulation of these Fox transcription factors in response to acute lung injury, however, has yet to be determined. We report here on the use of butylated hydroxytoluene (BHT)-mediated lung injury to demonstrate that HFH-11 protein and RNA levels were markedly increased throughout the period of lung repair. The maximum levels of HFH-11 were observed by day 2 following BHT injury when both bronchiolar and alveolar epithelial cells were undergoing extensive proliferation. Although BHT lung injury did not alter epithelial cell expression of HNF-3beta, a 65% reduction in HFH-8 mRNA levels was observed during the period of mesenchymal cell proliferation. HFH-8-expressing cells were colocalized with platelet endothelial cell adhesion molecule-1-positive alveolar endothelial cells and with alpha-smooth muscle actin-positive peribronchiolar smooth muscle cells.

Intermolecular and intramolecular interactions regulate catalytic activity of myotonic dystrophy kinase-related Cdc42-binding kinase alpha

Myotonic dystrophy kinase-related Cdc42-binding kinase (MRCK) is a Cdc42-binding serine/threonine kinase with multiple functional domains. We had previously shown MRCKalpha to be implicated in Cdc42-mediated peripheral actin formation and neurite outgrowth in HeLa and PC12 cells, respectively. Here we demonstrate that native MRCK exists in high-molecular-weight complexes. We further show that the three independent coiled-coil (CC) domains and the N-terminal region preceding the kinase domain are responsible for intermolecular interactions leading to MRCKalpha multimerization. N terminus-mediated dimerization and consequent transautophosphorylation are critical processes regulating MRCKalpha catalytic activities. A region containing the two distal CC domains (CC2 and CC3; residues 658 to 930) was found to interact intramolecularly with the kinase domain and negatively regulates its activity. Its deletion also resulted in an active kinase, confirming a negative autoregulatory role. We provide evidence that the N terminus-mediated dimerization and activation of MRCK and the negative autoregulatory kinase-distal CC interaction are two mutually exclusive events that tightly regulate the catalytic state of the kinase. Disruption of this interaction by a mutant kinase domain resulted in increased kinase activity. MRCK kinase activity was also elevated when cells were treated with phorbol ester, which can interact directly with a cysteine-rich domain next to the distal CC domain. We therefore suggest that binding of phorbol ester to MRCK releases its autoinhibition, allowing N-terminal dimerization and subsequent kinase activation.